Every man looks at other women. So there's nothing wrong with your guy in that regard. That said, the blatant staring he's doing in front of you is completely disrespectful and you are 100% right in being upset about it.
You need to let him know how you feel about this. A lot of guys don't realize how insulting and demeaning it is to check other women out in front of their girlfriends or wives. Your guy is clearly in that category, and so it's up to you to let him know that he shouldn't be. If you talk to him about it, hopefully he'll get the message and tone it down.
If not, something like that is grounds for a break-up.